Brook Floater ( Alasmidonta Varicosa)
Total Page：16
File Type：pdf, Size：1020Kb
COSEWIC Assessment and Status Report on the Brook Floater Alasmidonta varicosa in Canada SPECIAL CONCERN 2009 COSEWIC status reports are working documents used in assigning the status of wildlife species suspected of being at risk. This report may be cited as follows: COSEWIC. 2009. COSEWIC assessment and status report on the Brook Floater Alasmidonta varicosa in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vii + 79 pp. (www.sararegistry.gc.ca/status/status_e.cfm). Production note: COSEWIC would like to acknowledge Katherine A. Bredin and André L. Martel for writing the status report on the Brook Floater Alasmidonta varicosa in Canada, prepared under contract with Environment Canada, overseen and edited by Janice Smith and Dr. Dwayne Lepitzki, COSEWIC Molluscs Specialist Subcommittee Co-chairs For additional copies contact: COSEWIC Secretariat c/o Canadian Wildlife Service Environment Canada Ottawa, ON K1A 0H3 Tel.: 819-953-3215 Fax: 819-994-3684 E-mail: COSEWIC/[email protected] http://www.cosewic.gc.ca Également disponible en français sous le titre Ếvaluation et Rapport de situation du COSEPAC sur l’alasmidonte renflée (Alasmidonta varicosa) au Canada. Cover photo: Brook Floater — Provided by the author. Her Majesty the Queen in Right of Canada, 2009. Catalogue No. CW69-14/580-2009E-PDF ISBN 978-1-100-12944-0 Recycled paper COSEWIC Assessment Summary Assessment Summary – April 2009 Common name Brook Floater Scientific name Alasmidonta varicosa Status Special Concern Reason for designation A medium-sized freshwater mussel that is confined to 15 widely scattered watersheds in Nova Scotia and New Brunswick. This mussel was never abundant, usually representing only 1-5% of the total freshwater mussel fauna present. The habitat is subject to impacts (shoreline development, poor agricultural practices, and other water quality issues) with potential cumulative degradation on larger stretches of rivers. Populations appear to have been lost from two historic locations, although new populations have been formed recently. Because this mussel has disappeared from approximately half of its USA locations, the Canadian population now represents an important global stronghold for the species. Occurrence New Brunswick, Nova Scotia Status history Designated Special Concern in April 2009. Assessment based on a new status report. iii COSEWIC Executive Summary Brook Floater Alasmidonta varicosa Species information The Brook Floater, Alasmidonta varicosa (Lamarck, 1819), is a medium-sized freshwater mussel (50-65 mm long) with a kidney-shaped shell that is swollen in cross section. The shell is relatively thin, with a small patch of tiny ridges on the posterior edge that run perpendicular to the growth lines, creating a corrugated appearance. It is yellowish, greenish or brownish to black in colour, often with broad dark rays running from the top to the bottom. The Brook Floater has a cantaloupe-coloured foot that can be seen when the valves are still gaping as live individuals are removed from the water. Distribution The Brook Floater is distributed in eastern North America from northeastern Georgia through the eastern USA to central Nova Scotia and the southern half of New Brunswick, with a small discontinuity in northern New Hampshire and southern Maine. The species has disappeared from about half of the known locations in the USA. In Canada, the Brook Floater occurs in a relatively small number of rivers, including the St. Croix, Magaguadavic, Petitcodiac, Southwest Miramichi, Shediac, Scoudouc, Bouctouche and Kouchibouguacis watersheds in New Brunswick, and the Annapolis, LaHave, Gays, Wallace, East St. Marys and Salmon Rivers in Nova Scotia. Habitat The Brook Floater is usually considered to be a habitat specialist that requires running water environments such as shallow rivers or streams with moderate to high water flows. In New Brunswick it has only been found in rivers. In Nova Scotia, although primarily occurring in rivers, this species is occasionally found in small sandy-bottomed lakes with no evident water flow. It usually prefers sand or fine gravel substrates but is occasionally found in pockets of sand within cobble and rocky bottom areas. Although Brook Floater habitat in the USA is highly fragmented by dams and impoundments, this is not generally the case in Canada. iv Biology The male releases sperm into the water, which are drawn into the female’s mantle cavity during filter-feeding. Fertilization occurs in the female’s egg-filled marsupial pouches in the gills, where the glochidia (larvae) develop. Spawning occurs in summer, with brooding of the glochidia through fall and winter and release in spring. The glochidia are parasitic on fishes, attaching to their gills or fins. Potential host fishes in Canadian waters include Ninespine Stickleback, Yellow Perch, Golden Shiner and Blacknose Dace. After a period of development on the host fish, the juveniles drop off and burrow into the river bottom where they grow into adults. Like other mussels, this species feeds on bacteria, algae and other organic particles filtered from the water. Population sizes and trends The Brook Floater is never very abundant in rivers where it occurs, usually representing only 1-5% of the total freshwater mussel fauna present. In some Nova Scotia and New Brunswick rivers they are scarce, occurring at few sites within the river system with population estimates ranging from <100-<1000 individuals. Brook Floater abundance is higher in other rivers, ranging from 1000-10,000 individuals or possibly more. Although populations are disappearing throughout the USA, this does not seem to be the case in Canada, where only a few historically known populations were not re- confirmed during recent surveys. Recent discoveries of additional populations in the Maritimes likely reflect increases in survey effort rather than an increase in abundance and range. Limiting factors and threats Brook Floaters are threatened by aquatic habitat degradation in the form of silt, nutrient and sewage loads, due to poor agricultural and land management practices along a number of Maritime rivers where intensive agriculture and forestry are the principal forms of land use. Increased residential and cottage development, with associated damage to riparian and aquatic habitats, is also a potential threat to the typically small and disjunct populations of Brook Floaters. Special significance of the species About 8% of the Brook Floater’s global range occurs in Canada. With increased surveys in recent years, nine new populations have been discovered in the Maritimes at a time when populations are being lost in the USA. With declines south of the border, the Canadian population represents an important global stronghold for the species in a region with comparatively less habitat disturbance. v Existing protection or other status designations Brook Floater habitat is protected by provincial and federal legislation. The federal Fisheries Act prohibits the release of substances deleterious to fish, and activities that disrupt or destroy fish habitat. Forestry companies are required to leave unharvested zones along waterways, including rivers, streams and lakes, which help reduce siltation and inhibit summer water temperature increases. Under the Nova Scotia Environment Act, all wastewater discharges, construction of dams, and watercourse flow alterations are subject to review and approval. The Clean Water Act in New Brunswick protects surface waters from the effects of building construction, vegetation clearing, forestry activities, and the installation of dams or obstructions to water flow, by requiring an approved permit for such activities within 30 metres of a watercourse. Both provincial governments and the Canadian federal government require Environmental Impact Assessment Reviews for major developments, including those near waterways. vi COSEWIC HISTORY The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process. COSEWIC MANDATE The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens. COSEWIC MEMBERSHIP COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species.